This invention relates to a method forming copper-nickel-chromium bright electroplating being excellent in corrosion resistance for automotive or appliance, the surfaces of the parts thereof, and relates to the bright electroplating films obtained by said method.
In general, applying copper-nickel-chromium plating or nickel-chromium plating to automotives or appliances, or the surfaces of the parts thereof is most commonly used for improving the corrosion resistance of their basis materials along with for enhancing decorative effect by the combined use of painting etc.
Such copper-nickel-chromium plating or nickel-chromium plating are apt to lead to be suffered from flaw or crack at the surfaces thereof, and the existence of said flaw or crack causes corrosion progressing into the plating layer at the surface blemishes as shown in FIG. 1. Such corrosion has small anode area (nickel), therefore will provide greater corrosion current density which giving marked corrosion which also finally reaches basis material to form corrosion there. Such corrosion will possibly cause not only defects in appearance but also serious defects. To overcome such defects, it has been conducted that to employ thicker plating layers. However, a thicker plating layer has provided disadvantages either in the effective use of resources or in the costs concerned.
Then, in Japanese Patent Publication No. 15471/1981 it is disclosed that nickel platings were conducted by the use of a semi-bright nickel and bright nickel baths into which brightener and wetting agents were added, and then by the use of a nickel bath into which soluble amine compound, and aluminum or chromium ions being the most preferable metals selected from the metals in the groups III, V and VI or periodic table are added to allow minute particles to deposit on the nickel plating surface, and then chromium plating is applied thereon to provide the chromium plating surface with microporosity, resulting in small corrosion current density to obtain improved anticorrosive metal coatings. However, the number of micropores obtained by said invention are 1500-46500/cm.sup.2. The number of micropores of a chromium plating which has no possibility producing any clouding are 9300/cm.sup.2. Besides, when the concentration of metal ions are 0.5 g/l or more, there will occur burnt deposits harmful to plating. Therefore, when a large amount of such harmful metallic hydroxides are produced, there will be accompanied by disadvantages of requring the removal thereof by filtration.